Vehicle manufacturers have realized that it may be desirable under some conditions to automatically start and stop an engine of a vehicle. Stopping the engine can reduce fuel consumption, especially when the vehicle is stopped for longer periods of time, in stop-and-go traffic for example. However, during an automatic stop, a catalyst positioned in the exhaust downstream of the engine may become oxidized. Due to the catalyst being saturated with oxygen, water may not be available in the catalyst for the formation of hydrogen, which is used to control NOx upon a subsequent engine restart, thus degrading emissions.
The inventors have recognized the issues with the above approach and have developed an approach for improving emissions during an automatic engine start. In one embodiment, a method for an engine comprises during an automatic stop, injecting a water-containing fluid onto a closed intake valve of a cylinder while the engine is at rest, and on a subsequent restart, fueling the cylinder after at least one intake stoke and subsequent exhaust stroke are performed in the cylinder.
By injecting a water-containing fluid onto a hot, closed intake valve, the water may vaporize and be passed to the catalyst during a following intake stroke. By doing so, intake air may be displaced by the vaporized water in the cylinder, and the non-combusted exhaust reaching the catalyst prior to the initiation of combustion may be depleted of oxygen, reducing the saturation of oxygen in the catalyst. Further, the vaporized water-containing fluid may contribute water to the catalyst for hydrogen formation. In this way, emissions may be controlled during an automatic engine restart operation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.